X-ray tube cooling apparatus



Patented May 3, 1,949

2,468,942 iX-TRAYTUBE; EOLING'APPA'RATUS Wijhe.y Johannes Oosterkamp,l and helmus Vingerhoets, Eindhoven,

assigner-s to'y Hartford `Company,v- Hartford;

'Antonius' IW-il- Netherlands,

National :Bankand Trust Conn., as trustee --Application July 1,- 1946, .Serial No.. 680,612 n the Netherlands March 15,' 1943 =`Section 1, Public" Law 690,,Augustu8f1946 A-llatent expires March 15., 1963 6 Claims. l (Cl. Z50- 143) ilibe load WhiChanX-ray tube can withstand forhal'comparatively longtime is va `function of thevamountiohheat,carried-oli per unit of time. Fontesting materials ,and -for the investigationv of technical constructions tubesare of importance Whichcan remain operativeior the duration of the investigation, which in. most cases extends over a few minutes but `whichin some cases may lastzfmuchlonger. ,.Withtimes of load of .this orden'fofnmagnitudeutheldistrbution of heat in the anode isstationary,that is to say independent ottime andthence solely dependent upon the dimensions and` the :coefficientsof thermal conductivity ,of the. k'materialsused.

If the load is giVen a sufficiently low value, an ordinary technicalX-ray tube may be used for thesevinvestigations. In thisqcase, however, the possibilities tot application l`are very. smallv and are limitedtorinvestigations oi thin vlayers of material and thin-walled constructional parts. According :as thethickness p-ofthe objects to be investigated increases., the tube` must be capable of withstanding a higher load. A comparatively high load is permissible with such-tubes, it is true, if thesurfaeeof impact of the-electrons on the anode is given a larger size and .thelarger amount-ot'heat thus, produced inthe anode. can be carried away by the cooling system. As .a result of thei largefocus, the images lobtained are highly unsharp-and this is detrimental to theI accuracy of the investigation. Applicant has found that vthe known .constructions comprising ananode which radiates heat ,at high temperature, and those comprisingan anode havinga high heat capacity, :which is cooled by liquid, orof which the anode -is in intimate thermal relation Ywithl a body having a largeyheat-radiating surface, .cannot satisfy the requirements imposed for the said purpose as regards quality of image andA load; capacity.

1n; order, to increasegthe' load continuously permissible, an X-ray tube is'already knownwhich compr-leesl a disc-shaped -anode constituted by a thin metal plate, the heat produced in this plate asa result of the. impact .of electrons being carriedaway on. theside ywhich is remote from. the surface .of impact. ,In this casel the disc-shaped anode must be; cooled very thoroughly since the surface available for the `transmission of heat. is much; smaller than in the mst-mentioned .constructions Thus they back of the anode plate is cooled-with the aid yof a liquid flow, the liquid being;conducted.with, great speed along thelsurface. Fortheglspeed;of':ithe liquid litis decisive that therowns must he. turbulent, it being-necesa 21;.2 sarythat between the t. rbulent,l core and thecontactsurface therashould beca-layer in which the flowing is laminar. Consequently; the 'evacuation. of heat takes,[place: in twolstages:

(l) By conduction" bythe laminar limiting layer (2) By convection in theturbulent core of .the

flow.

"A.good'conductlonofaheatlbythe laminar limitingV layerwmayzbeeobtained bywutili'zing a, liquid hauingaa l highI thermal: conductivity. f For `the second factor `the specific' fheatvperzunitot volume and the speed of the'iliquidareethesprincipail characterizing magnitudes. f'fThespced---of the liquidiflow.:is` flimited'byflthe height :of the pressure,:,whiel1;ls lrelatedz-.to the: section lof fthe conductors and the viscosityfofrthe -liquid.

' This :invention relatesv-to an-:X-ray tubeAv comprising: ,anv fanode, 4theft-.surface of 'impact 'y of the electrons beingconstitutedbyrfa-thin metal plate and the yheat@ :producedifin the flatter being carried awayzon .the `side fwhichi :is remote.4 from the surface 'struck the electrons.

:The :present `nverrtion :purports vto improve the evacuation of heatnofi this:l tube in such manner that .it ycan be` Vloaded Veryff strongly.

.Acoordingtotthelinvention, that side of the anode from whichrtheheat `is carried off is brought into-A intimate thermal# relation with a cooling-body 'the surfaceofwwhich streaks along the anode, .thel intimate thermal relation between-the anode f. andl'the Lcooling body being effected by-a thin layer'of afliquidhaving a great thermal conductivity.r The-transmission of heat from'the anodewto the 1cooling body is better, according as 'the vcoencient'-oi- 'lthermatconductivity of,` the-material between the ltwo surfaces has a higher Avalue. Materials-serviceable for this purpose areA liquid metals-orl metalfalloys such, -for exan'rple,y as 1 mercury.

construction is obtained if the space which exists between the cooling body and the housing is filled with a liquid similar to that which is present between the anode and the cooling body, so that this liquid also serves for the transmission of heat from this body to the wall of the housing. It is advisable that use should be made of a cooling body consisting of metal having a high thermal conductivity such, for example, as copper, and a high heat capacity. The advantage thereof is that the heat which is quickly distributed in the body, due to which the heat emission takes place over as large a surface as possible and the variation in temperature in the cooling liquid may be small.

In many cases the focal spot, that is the spot of the anode which is struck by electrons will have an elongated shape, the longest dimension of which as viewed in the direction of the emanating X-ray beam is observed as shortened. In this case it is advantageous for a good transmission of heat from the anode to the cooling body if the direction of motion of that surface of this body which streaks along the anode is at right angles to the longest dimension of the spot of impact of the electrons.

The cooling body is preferably realized as a rotary member and is given the shape of a cylinder or a disc. The cooling of this member may alternatively be effected by a separate liquid, for example by making the cooling body hollow and by supplying and carrying off the cooling liquid through the axis of rotation.

The invention Will be explained more fully by reference to the accompanying drawing showing, by way of example, one form of construction of a tube according thereto.

Xray tube i comprises a cooling device 2 and is constituted by a metal portion 3 provided with an aperture l closed by a thin metal plate 5 of tungsten. This metal plate, which constitutes the anode, serves as the disc of impact for the electrons and is heated under the action of the impact of electrons. The heat produced in the disc is carried away at its back and is transmitted to a cooling body 8 by means of a liquid which completely lls the casing E of cooling device 2 and which is also present between anode 5 and cooling body 8. `The presence of this liquid is not sufficient quickly to carry oi the heat from the heated surface, although in the example shown the whole heat transport is effected via the liquid. The heat is emitted by the liquid to the wall of casing 6 which cornprises cooling ribs l to facilitate the radiation of heat to the surrounding air. The emission of heat may be increased by means of artificial cooling of casing '6, for which purpose it may be provided with an envelope, a liquid` or a gaseous cooling agent being led through the space which exists between the casing and the envelope.

Cooling body 8, which is preferably of copper, is shaped in the form of a disc and can rotate about a shaft 9 which is led to the exterior through the wall of casing t of the cooling device with the aid of an obturating ring l!) for the liquid. When the X-ray tube is operative, disc 8 is rotated; shaft 5 may be driven by means of a motor which may be united to form one whole with the cooling device. The number of revolutions of disc 8 may be, for example, 50 p-er second.

Due to the fact that a continuously changing part of the conical surface of cooling body 8 is opposite the anode, the heat is rapidly carried away from the latter and absorbed by the cool- 4 ing body. The heat absorbed by this body is retransmitted, by means of the liquid present in the casing, to the wall of the casing, which com prises cooling ribs 'I for the purpose of facilitating the emission of heat to the surroundings.

It is advisable that the metal member 3 should be arranged in such manner that between its surface and the heated surface of the disc of impact there exists only a small intermediate space so that at this place exists a thin layer of the liquid. The conditions for the obtainment of the highest possible increase in load relatively to the known tubes are best satisfied if this spacing is as small as possible and, for example, so small that the surface of the metal member does not contact with the surface of the disc of impact inthe case of flection of the latter due to heating by electrons. The difference of temperature in the thin liquid layer may consequently be Very small.

The metal portion 3 of the X-ray tube is connected to a glass portion l l of the wall, comprising a re-entrant part I2. The latter carries a collecting device i3 containing an incandescent cathode lli which is heated by electric current, for which purpose serve supply conductors I5 and I6 which are led in a vacuum-tight manner through the glass stem Il.

The cooling device may be fastened to the tube by means of a flanged connection I8, for which purpose the extremity of the metal portion 3 of the tube has a larger wall thickness. Consequently, the tube may be. completely finished and exhausted before the arrangement of the cooling device.

Portion 3 of the wall is provided with an aperture 22 which is closed by a thin glass window serving for the transmission of active rays.

Several other constructions of the cooling system are possible, for which also use is made of the invention, so that the inventive idea is by no means limited to the form of construction shown in the iigure.

What we claim is:

l. An X-ray tube, particularly adapted for prolonged loads, comprising a cathode, an anode comprising a target heated on the surface facing the cathode by electrons from the cathode, and to be cooled by removal of the heat through the rear surface thereof; and means for cooling the anode by rapid removal of the heat therefrom, said means including a body of liquid having a high thermal conductivity in intimate thermal contact with the rear surface of the anode, and a rotatable disc-shaped cooling body disposed so its peripheral edge is immersed in the liquid and closely adjacent the rear surface of the anode plate and separated therefrom by a lm of the liquid.

2. An X-ray tube as in claim 1, in which mercury is used as the liquid to transmit heat from the anode to the cooling body.

3. An X-ray tube as in claim 1, in which the heat transfer liquid and the cooling body are enclosed in a Vessel having heat-radiating surfaces, and the heat transfer liquid engages a substantial area of the inner surface of the vessel to conduct heat thereto for dissipation from thev outer surface of the vessel.

4. An X-ray tube as in claim 1, in which the anode plate is at an angle to the cathode and the electron beam impinges on the target to form a line focus having an axis in a given direction, and the direction of motion of the cooling body is at right angles to said axis of the electron spot.,`

5. An X-ray tube as in claim 1, in which the REFERENCES CITED heat transfer liquid and the cooling body are The following references are of record in the enclosed 1n a, vessel, and the rotatable cooling me of this patent. body is mounted on a. rotatable shaft extending through a wall of the vessel. 5 UNITED STATES PATENTS 6. An X-ray tube as in claim 1, in which the Number Name Date anode plate has a given thermal mass, and the 1,095,121 Mannheim Apr. 28, 1914 cooling body has a substantially greater thermal 1,180,998 Gibson Apr. 25, 1916 mass than the given thermal mass of said anode. 1,635,928 Morrison oet, 2, 1928 10 1,705,033 smith Mar. 12, 1929 WIJBE JOHANNES OOSTERKAMP 1,972,414 Worden Sept. 4, 1934 ANTONIUS WILHELMUS VINGERHOETS. 2,075,146 Sergeeff Mar. 30 1937 

